docs: def _tree2str(self, tree, root=True):
          """ Convert parsed condition tree back to a (printable) string.
          """
          try:
              # Keep strings as they are
              return '' + tree
          except (TypeError, ValueError):
              flat = ' '.join(self._tree2str(i, root=False) for i in tree)
              return flat if root else "[ %s ]" % flat